1. Field of the Invention
This invention relates to carpet, especially automobile carpet, precoat compositions and more particularly, it relates to highly filled hot-melt adhesive compositions based on defined ethylene/vinyl acetate copolymers made with selected telogens blended with processing oil.
2. Description of the Related Art
Tufted carpets typically have a layer of a polymeric composition on their backside. These polymeric compositions are commonly adhesives applied as a hot-melt. This polymeric backside layer provides various desirable characteristics to the carpet as a whole. Such characteristics will differ depending on the type of carpet. Industrial carpet requirements for instance are generally more stringent than domestic carpet requirements. Automotive carpet has different requirements again.
While such polymeric hot-melt adhesive layers can be applied directly to the backside of the carpet, the properties required of the backside layer often require a composition whose flow characteristics do not allow sufficient adhesion and `wetting` of the carpet yarn bundles necessary to maintain the integrity of the carpet in use. An alternative is to use an intermediate `precoat` adhesive layer between the carpet tufting and the `main` backside layer. Such precoats are compositions designed to penetrate the tufts, wet the filaments of yarn bundles, and at the same time adhere to the main carpet backside layer. A precoat must be fluid enough to penetrate the bundles, yet have sufficient strength to provide good wear characteristics to the carpet.
Precoats for general carpet use may be any of a large number of polymers. Examples of such polymers are given in U.S. Pat. No. 3,684,600, where ethylene/vinyl acetate copolymers containing 15-35 weight percent ester are described as being especially preferred. Typically, these are compounded with wax which serves to lower the viscosity. For automotive carpet use, polyethylene and ethylene/vinyl acetate resin alone (without filler or other ingredients) have been used. The latter has superior adhesive qualities, and is particularly useful when the main layer is also based on a composition containing ethylene/vinyl acetate. However, ethylene/vinyl acetate resin is relatively expensive to use alone and attempts have been made to reduce costs by blending with high levels of cheap extenders such as fillers. As much as about 60 wt. % filler may be needed to provide an economically viable composition. But, fillers increase viscosity and it has heretofore not been found possible to obtain highly filled ethylene/vinyl acetate compositions with a suitable balance of fluidity and mechanical properties to serve as an adequate precoat.
U.S. Pat. No. 3,583,936 discloses a backsizing composition which can be used without a precoat, and approaches the fiber penetration properties of a precoat. The composition is preferably based on ethylene/vinyl acetate polymer. However, it may contain only up to 40 wt. filler. It also contains at least 10 wt. % wax and also other polymeric components all of which are expensive relative to filler cost.
The main carpet backside layer which provides other use characteristics to the carpet may also be based on filled ethylene/vinyl acetate copolymers. In the case of automotive carpet, for instance, these characteristics may include sound deadening and formability to the contours of the car as well as the overall `hand` of the carpet. Sound deadening is achieved by using a very high filler content which may be as high as 70 wt. % of the total composition. Thus, a filled ethylene/vinyl acetate copolymer main backside layer composition has similar ingredients to compositions which are of interest in precoat layer compositions. Useful polymeric compositions for the main automotive carpet backside layer are described in U.S. Pat.No. 4,191,798 which is hereby incorporated by reference. Preferred compositions comprise a blend of ethylene/vinyl acetate, processing oil, and calcium carbonate or barium sulfate. While these compositions are ideal for the overall carpet requirements, they do not provide good bonding and wetting to the filaments in the fiber bundles because they are too viscous. As a result they cannot be used as the only backside layer. Melt indices of these main carpet backside compositions range from 1.79 to 9.65, whereas much higher melt indices, at least 60, are necessary for tuft penetration and wetting. Attempts to use a lower viscosity version of such compositions as the only backside layer by utilizing higher melt index ethylene/vinyl acetate polymeric components, have not proved successful, since properties become inadequate. As a result, lower viscosity precoats are generally used as an intermediate layer between the carpet tufts and the main carpet backside layer.
The mechanical properties required of a precoat adhesive material generally need not be quite so good as those of the main backside layer. As a result, despite unsuitability as a main backside coat, lower viscosity versions of such main backside layer composition have also been considered as a precoat. Such compositions would have the high filler necessary to lower cost, and, because of the overall composition similarity, would adhere well to the higher viscosity main backside layer. However, even as a precoat composition, such compositions have been found inadequate.
U.S. Pat. No. 4,434,261 discloses an extrudable, self supporting hot-melt adhesive sheet which has a melt index of 10 to 500 and may contain, amongst many other polymers, ethylene/vinyl acetate copolymer blended with 2-30 wt. % plasticizer and 20-80 wt. % filler. In the only example, a composition with 30 wt. % ethylene/vinyl acetate copolymer, 55 wt. % filler and 15 wt. % oil has a melt index of 76, and moderately good mechanical properties. There is no indication the compositions disclosed would provide adequate carpet precoat adhesives especially at filler levels above 60 wt. %. There is no disclosure that the ethylene/vinyl acetate copolymer used was made using any telogen.
There remains a strong need to provide a low viscosity ethylene/vinyl acetate based precoat adhesive which is inexpensive by virtue of very high levels of cheap filler, yet has adequate mechanical properties and which is especially suited for use in automotive carpets.